This invention relates to a crank angle detector for an engine. Particularly, this invention relates to a crank angle detector adapted to mask unnecessary angular signal output from a pair of crank angle sensors and which become a burden to a controller.
As the crank angle detector of this kind generally known, there are detectors of an angular control system and a time control system.
The crank angle detector of the angular control system is disclosed in Japanese Patent Application Laid-Open No. 60-17311. The detector counts a number of projections formed on an outer periphery of a rotor plate synchronously rotating with a crank shaft to calculate an engine speed, or measure an ignition timing.
On the other hand, the crank angle detector of the time control system is disclosed in Japanese Patent Application Laid-Open No. 60-120918. As shown in FIG. 1, a crank angle sensor 3 detects projections 2a, 2b and 2c spaced at each predetermined angle .theta.1, .theta.2 and .theta.3 (e.g., .theta.1=112.degree., .theta.2=80.degree., .theta.3=10.degree.) from a top death center (T.D.C.) on an outer periphery of a rotor plate 2 secured to an end of a crank shaft 1. A controller 4 such as a microcomputer measures time elasped between the projections 2a and 2b. Thus, the controller 4 calculates the engine speed from a calculated angular velocity. Furthermore, the controller 4 sets the projection 2b as a reference of an ignition timing, and sets the projection 2c as a fixed ignition angle at starting.
A cam rotor 6 is axially secured to a cam shaft 5 rotating at half the speed of the crank shaft 1. Furthermore, another crank angle sensor 3b detects projections 6a equidistantly formed on an outer periphery of the cam rotor 6 to discriminate a cylinder number.
As shown in FIG. 2, the signals .theta.1, .theta.2 and .theta.3 obtained by detecting respective projections 2a to 2c of the rotor plate 2 are output from the crank angle sensor 3a.
Accordingly, as shown in the flowchart of FIG. 3, the controller 4 reads a cam pulse by detecting the projection 6a of the cam rotor 6 at a step ST1. Then, at a step ST2, the controller 4 discriminates and reads a crank pulse thereinto. At the subsequent steps of the flowchart corresponding to the projection shown by single dotted lines in FIG. 3, a judgement as to what crank pulse has been read thereinto at the step ST2 is made in accordance with the cam pulse at the step ST1. For example, when the crank pulse is first input after the cam pulse, the crank pulse is judged to be a .theta.1 pulse at a step ST3, respective proceedings at steps ST10 and ST11 are executed as an interrupt flag of the .theta.1 pulse. When the crank pulse subsequent to the .theta.1 pulse is judged to be .theta.2 pulse at a step ST4, an interrupt processing of .theta.2 pulse is executed at steps ST20 and ST21. When it is judged that the crank pulse subsequent thereto is not the .theta.1 and .theta.2 pulses, a judgement is made as to whether or not that crank pulse is a .theta.3 pulse (step ST6). As a result, when the crank pulse is the .theta.3 pulse, the interrupt of the .theta.3 pulse is executed at a step ST7 at the time of starting the engine. When the crank pulse read in at the step ST2 is the .theta.3 pulse (fixed ignition signal), the judgement at the step ST6 is defined as a processing for making a judgement as to whether or not a signal processing of the .theta.3 pulse is required.
In this instance, the .theta.3 pulse (fixed ignition signal) is required only at starting the engine, but is not required after complete firing.
However, since the above-mentioned respective crank pulses are sensed by the single crank angle sensor 3a, they are all input to the same interrupt request terminal. Accordingly, when the controller 4 is provided with the .theta.3 pulse after starting, a judgement will be made as to whether or not interrupt processing of the .theta.3 pulse is required. The load upon the software is therefore increased accordingly.
When the engine speed is low, the interval between crank pulses is long and there is a relative margin in the processing ability. On the contrary, when the engine speed reaches a higher value (e.g., 6000 to 7000 r.p.m.), the interruption load upon the software becomes large. Thus, it is likely that the computational processing ability of a microcomputer as the controller would become insufficient, and control performance for the engine would be lowered as a result.
It is to be noted that when a microcomputer having a fast computational processing speed and a large capacity is used, insufficiency in the computational processing ability is eliminated, but the cost is increased accordingly